// 创建symbol
let s = Symbol();
console.log(s, typeof s); //Symbol() 'symbol'

let s2 = Symbol('seven');
console.log(s2); //Symbol(seven)
let s3 = Symbol('seven');
console.log(s2 == s3); //fasle

// Symbol.for创建
let s4 = Symbol.for('seven');
console.log(s4, typeof s4); //Symbol(seven) 'symbol'

// 不能与其他数据进行运算
// let result = s + 100; //Cannot convert a Symbol value to a number
// let result = s + '100'; //Cannot convert a Symbol value to a string

